Dinosaur Tracks at Cañadón De Las Campanas and Villa El Chocón Area (Late Cretaceous, Candeleros Formation), Patagonia, Argentina

Volumen 77 (3): REVISTA DE LA DESARROLLOS RECIENTES EN ICNOLOGÍA ARGENTINA ASOCIACIÓN GEOLÓGICA ARGENTINA www.geologica.org.ar Septiembre 2020

Dinosaur tracks at Cañadón de las Campanas and Villa El Chocón area (Late Cretaceous, Candeleros Formation), Patagonia, Argentina

Verónica KRAPOVICKAS1, Alberto C. GARRIDO2,3, and Juan I. CANALE4

1IDEAN-CONICET, Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires 2Museo Provincial de Ciencias Naturales “Prof. Dr. Juan A. Olsacher" Zapala, Neuquén. 3 Centro de Investigación en Geociencias de la Patagonia – CIGPat, Universidad Nacional del Comahue. Neuquén. 4CONICET- Área Laboratorio e Investigación, Museo Paleontológico “Ernesto Bachmann”, Villa El Chocón, Neuquén.

Email: [email protected]

Editor: Graciela S. Bressan y Diana E. Fernández Recibido: 15 de abril de 2020 Aceptado: 11 de septiembre de 2020

ABSTRACT

Several locations are known along the coast of the Ezequiel Ramos Mexía Dam, Neuquén province in Northwestern Argentinian Pa- tagonia, comprising one of the richest dinosaur-tracking areas in South America. In this contribution we study a total of 166 dinosaur footprints and 31 dinosaur trackways recorded at the base of the Candeleros Formation (Cenomanian) from a new tracksite - Cañadón de las Campanas - and other localities nearby the Villa El Chocón area. The dinosaur footprints identified correspond to six morphotypes assigned to two ichnotaxa and three others are left with open nomenclature: Bressanichnus patagonicus, cf Brontopodus isp. (Sauropodichnus giganteus), large U-shaped tridactyl footprints (Limayichnus major), medium-siz ed tridactyl footprints and small- sized tridactyl footprints. The ichnotaxa S. giganteus and L. major are considered nomen dubium. Particularly, B. patagonicus presents two morphologies at the posterior margin of the footprint (rounded and narrow) most likely related to varying gaits and/or changing behavior. As a result, the herein presented ichnofauna is interpreted as produced by non-avian theropod of varied sizes (large sized = large U-shaped tridactyl footprints, medium to large size = B. patagonicus, medium size = medium-sized tridactyl footprints and small size = small-sized tridactyl footprint) and one large-sized sauropod dinosaur (cf. Brontopodus isp.).

Keywords: Vertebrate ichnology, Mesozoic, Neuquén Basin, sauropods, non-avian theropods.

RESUMEN

Huellas de dinosaurios del Cañadón de las Campanas y el área de la Villa El Chocón (Formación Candeleros, Cretácico Tardío) Pa- tagonia, Argentina Numerosos afloramientos a lo largo de la costa del Embalse Ezequiel Ramos Mexía, provincia de Neuquén en el noroeste de la Pata- gonia argentina, comprenden uno de los sitios icnológicos de dinosaurios más ricos de Sudamérica. En esta contribución estudiamos un total de 166 huellas y 31 rastrilladas de dinosaurios registradas en la base de la Formación Candeleros (Cenomaniano) de la nueva localidad Cañadón de las Campanas y en otras áreas en los alrededores de la Villa El Chocón. Las huellas de dinosaurios identifica- das corresponden a seis morfotipos asignados a dos icnotaxa y tres morfotipos mantenidos en nomenclatura abierta: Bressanichnus patagonicus, cf. Brontopodus isp. (Sauropodichnus giganteus), huellas tridáctilas grandes en forma de U (Limayichnus major), huellas tridáctilas medianas y huellas tridáctilas pequeñas. Los icnotaxones S. giganteus y L. major son considerados nomen dubium. Particularmente, B. patagonicus presenta dos morfologías del margen posterior de las huellas (redondeado y angosto) posiblemente relacionados con variaciones en el tipo de marcha y/o cambios en el comportamiento. Como resultado se interpreta a la icnofauna aquí presentada como producida por dinosaurios terópodos no avianos de diferentes tamaños (grande = huellas tridáctilas grandes

447 Revista de la Asociación Geológica Argentina 77 (3): 447-462 (2020) en forma de U, mediano a grande = B. patagonicus, mediano = huellas tridáctilas medianas y pequeño = huellas tridáctilas pequeñas) y un dinosaurio saurópodo de gran tamaño (cf. Brontopodus isp.).

Palabras Clave: Icnología de vertebrados, Mesozoico, Cuenca Neuquina, saurópodos, terópodos no avianos.

INTRODUCTION at the NW margin of the Ezequiel Ramos Mexía Dam. The focus of this work is to evaluate the footprint record in terms The Candeleros Formation records one of the most sig- of richness of morphotypes, ichnotaxonomy and possible pro- nificant dinosaur footprint assemblages of South America in ducers. terms of abundance, diversity, and excellent preservation of dinosaur tracks. The ichnoassemblages are recorded along the coast of the Ezequiel Ramos Mexía Dam and in the north GEOLOGIC SETTING of Neuquén province in Agua de Tuco area, Argentina. The pioneer ichnologic studies were carried out by Calvo (1989, The Neuquén Group (Stipanicic et al. 1968) conform a 1991) at the South extreme of the Ezequiel Ramos Mexía succession of continental deposits of fluvial, aeolian and Dam nearby Picún Leufú (Fig. 1). Later other studies were shallow lacustrine origin of approximately 1,200 m thick (Ca- performed around the same area (Calvo 1999, Calvo and zau and Uliana 1973). They were accumulated during Ceno- Mazzeta 2004) and at the northwest and central east margin of manian-Early Campanian times in the Neuquén foreland ba- the Ezequiel Ramos Mexía Dam at the Villa El Chocón and la sin system (Franzese et al. 2003). Buitrera areas respectively (Calvo and Moratalla 1998, Calvo The litostratigraphy framework of the group was proposed and Lockley 2001, Candia Halupczok et al. 2018) and, more by Cazau and Uliana (1973) and latter modified by Ramos recently in a new locality between Chos Malal and Añelo cities (1981) and Garrido (2010). The basal unit of the Neuquén in the central-north of Neuquén province (Heredia et al. 2019, Group is the Río Limay Subgroup that comprises the Cande- 2020). So far, a total of ten ichnogenera of pterosaur, non-avi- leros and Huincul Formations. The Río Neuquén Subgroup an theropod, sauropod and ornithopod tracks were described. comprise the Cerro Lisandro, Portezuelo, Los Bastos, Sier- Eight were presented to describe the Picún Leufú material ra Barrosa and Plottier Formations. Finally, the Río Colorado (Calvo 1991, 1999, Calvo and Moratalla 1998) and one was Subgroup integrated by the Bajo de la Carpa and Anacleto introduced to describe material of a norther area (Heredia et Formations. al. 2020). In addition, in the Candeleros Formation other three The Candeleros Formation is the basal litostratigraphic unnominated morphotypes (Krapovickas et al. 2007, Krapo- unit of the Neuquén Group (Upper Cretaceous) and its type vickas 2010, Heredia et al. 2019) and multiple tracks in cross locality is located at the Los Candeleros hill, southeast of the section (Candia Halupczok et al. 2018) are recorded. Cerro Lotena south of Neuquén Province (Wichmann 1927). Regarding the vertebrate body fossil record of the Can- The thickness of the sequence reaches up to 300 m of coarse- deleros Formation, it comprises a great diversity of forms, to medium-grained massive sandstones and conglomerates including dipnoan fishes, pipimorph amphibians, chelid- tur of reddish to violet color and it was interpreted as deposited tles, uruguaysuchid crocodylomorphs, basal snakes, iguanian in braided fluvial systems and by eolian processes. The unit is squamates, sphenodontians, pterodactyloid pterosaurs, sau- Cenomanian in age (Vergani et al. 1995, Leanza et al. 2004) ropod and theropod dinosaurs, and mammals, recovered in and overlies discordantly the Lohan Cura Formation of early the central-south of Neuquén and west of Río Negro provinc- Cenomanian age. At Villa El Chocón the unit comprises an es (Calvo and Salgado 1995, Coria and Salgado 1995, Calvo approximately 100 m thick alluvial sequence of composed by 1999, Ortega et al. 2000, Baez et al. 2000, Apesteguıá and fine-grained red to violet sandstone, greywacke and siltstone Novas 2003, Apesteguıá et al. 2005, 2007, Apesteguıá and with thin evaporitic intercalations and, thin tuff levels occa- Zaher 2006, de la Fuente et al. 2006, Otero et al. 2011, Rou- sionally preserved (Fig. 2). The succession is attributed to gier et al. 2011, Haluza and Canale 2013, Novas et al. 2013, playa lake deposits, ephemeral fluvial channels, and aeolian Canale et al. 2016). dunes in a distal terminal fan context (Garrido 2010, Sánchez Herein we present a study of the dinosaur tracks preserved and Asurmendi 2015, Candia Halupczok et al. 2018). The di- in the vicinity of the Villa El Chocón area (Villa El Chocón and, nosaur footprints are preserved at the base of the Candeler- Balneario Villa El Chocón) and Cañadón de las Campanas os Formation on playa lake and wet interdune deposits (Fig.

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Figure 1. a) Geologic map of the Neuquén Group along the margins of the Ezequiel Ramos Mexía Dam, Neuquén Province. Modified from Garrido 2005 and Krapovickas 2010. Study area: b) Balneario Villa El Chocón (BVC); c) Villa El Chocón (VC); d) Cañadón de las Campanas (CC).

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2) (see Krapovickas 2010). Wet interdunes are recorded by moderated sorted, medium- to fine-grained sandstone with a low percentage of mud matrix. Adhesion ripples, fluidization structures, and polygonal desiccation mud-cracks on mud- drapes are frequently preserved. Playa lakes are represented by intercalations of massive to laminated mudstones and massive, laminated to thin-bedded fine-grained sandstone. They are arranged in individual 5-15 cm thick tabular beds. Polygonal desiccation mud-cracks, deformational structures, and small gypsum fragments are frequently preserved. It is also observed local obliteration of sedimentary structures due to high bioturbation. We studied three major areas (tracksites): 1) Villa El Chocón (39°15’56.2’’S, 68°46’12.7’’W), 2) Balneario Villa El Chocón with three tracking levels of lateral continuity (Tl1 39°16’22.0’’ S, 68°49’16,.’’W; Tl2 39°16’20.0’’ S; 68°49’43.5’’ W; Tl3 39°16’19.5’’ S; 68°49’28.8’’ W) and 3) Cañadón de las Campanas preserved in five tracking levels of lateral continuity (Tl1 39º20’05.6’’S; 68º56’06.1’’W; Tl2 39º19’32.6’’S; 68º56’43.1’’W; Tl3 39º19’04.3’’S; 68º56’53.0’’W; Tl4 39º18’35.3’’S; 68º57’08.6’’W; Tl5 39º18’27.4’’S; 68º57’26.9’’W) (Fig.1). Particularly, at Cañadón de las Campanas the tetrapod footprints preserved corresponds to B. patagonicus and cf. Brontopodus recorded in playa lake and wet interdune deposits (Krapovickas 2010). At Villa El Chocón medium- and small- sized tridactyl footprints in playa-lake deposits (Krapovickas et al. 2007). At Balneario El Chocón, B. patagonicus, cf. Bron- topodus, and large u-shape tridactyl footprints are recorded in playa-lake deposits (Krapovickas 2010).

MATERIALS AND METHODS Figure 2. Schematic log of the Candeleros Formation at the Villa El Cho- cón area. Modified from Garrido 2005. A total of 166 individual footprints and 31 trackways are studied in this contribution. Most of the material is preserved pression on the substrate of the autopodium or part of the in situ. Plaster casts of individual footprints and maps of the autopodium of a tetrapod. Parameters to describe footprints tracking surface are performed to preserve some of the most are: Track length (TL), measured parallel to the axis of the significant morphologies. Maps are made as 1m x1m grid and longest digit from the most anterior point to the most posterior 1:1 scale map in transparent polyaniline. Two plaster casts point of the footprint. Trackwidth (TW), measured parallel to are housed under MCF-PVPH-818, MCF-PVPH-819, and one the transverse axis between the furthest medial and lateral map in transparent polyaniline under MCF-PVPH-817. Mea- points. Digit length (L), measured from the tips of the individ- surements are directly taken over the studied material. Insti- ual digits to the posterior outline of the footprint (Mccrea and tutional abbreviation: Museo Carmen Funes, Plaza Huincul, Sarjeant 2001). Digit width (W) numbered in correspondence Neuquén Province, Argentina (MCF-PVPH). to each digit number as for digit length (e.g., LIV, WIV for the Parameters to describe tracks and trackways are mostly fourth digit). Interdigital angle (Div), measured from where the used following Leonardi (1987) and Thulborn (1990). Track longitudinal axis of one digit intersects the posterior outline is employed as a synonym of footprint and defined as the im- of the footprint and, to the longitudinal axis of another digit

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(Currie 1981). Parameters to describe trackways are oblique pace (P), stride (S), pace angulation (P ang) (Leonardi 1987). In this work, trackway parameters were measured between pes. Extended tables of footprint and trackways morphometric data are available in (Krapovickas 2010). In sauropod tracks and trackways, heteropody [(manus area/pes area) x 100] is based on Lockley et al. (1994a), and the pes trackway ratio (PTR) to evaluate gauge patterns [(FW /TW) x 100], as proposed by Romano et al. (2007).

SYSTEMATIC ICHNOLOGY

Bressanichnus patagonicus Calvo 1991 Figs. 3-6. Tables 1-4. Material: 108 footprints within 21 trackways preserved at Cañadón de las Campanas (CC) and Balneario Villa El Chocón (Table 1.1-1.6). MCF-PVPH-818 plaster cast of CC- Tl4-R2-1, MCF-PVPH-819 - plaster cast of Nq-CC-Tl2-R1-2, MCF-PVPH-817 map of the trackway CC-Tl2-R4. Description: Tridactyl footprints with well-defined claw

Figure 4. Bressanichnus patagonicus tracks and trackways recorded at Tl2 Cañadón de las Campanas.

marks of a parasagittal biped animal of medium to small size. The impression of the central digit (III) is medially curved and longer that the lateral digits, that sometimes are not well defined (Fig. 3b-c). The impression of digit III shows at least two well defined digital pads. Digits II-III hypex is positioned more Figure 3. Bressanichnus patagonicus preserved at the Candeleros For- mation: a) CC-Tl4-R2-1, left impression. Note the rounded posterior mar- backward than that of digits III-IV. The posterior margin of the gin of the footprint; b) CC-Tl4-R1-3, left impression. Note the narrow pos- footprint is sub-rounded (Fig. 3a, c) to elongate (Fig. 3b, d) terior margin of the footprint; c) CC-Tl2-R1 -2, right impression. Note the rounded posterior margin of the footprint; d) BC-Tl2-R3-2, left impression. and varies within the same trackway. Digital impressions are Note the rounded posterior margin of the footprint. Scale: white area = relatively narrow. The average total length of the footprints is 1cm.

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Table 1. Footprint morphometrics of B. patagonicus. Cases with a rounded posterior margin of the footprint. 95 footprints measured. Measures in cm.

FL FW DIV ANG II-III ANG L II L III L IV W II W III W IV III-IV MAX 44.00 33.00 82.00 45.00 42.00 36.00 44.00 32.00 8.00 8.00 5.00 MIN 19.50 12.00 36.00 20.00 15.00 3.00 8.50 2.60 2.30 3.50 2.50 AVG 28.70 20.80 59.00 32.00 29.00 18.21 23.04 14.83 3.76 5.18 3.54 SD 4.55 3.74 10.00 6.00 7.00 10.71 10.13 8.54 1.52 1.12 0.99

Table 2. Trackway morphometrics of B. patagonicus. Cases with a roun- Table 4. Trackway morphometrics of B. patagonicus. Cases with a narrow ded posterior margin of the footprint. 19 trackways measured. Measures posterior margin of the footprint. 1 trackway measured. Measures in cm. in cm. PACE STRIDE P ANG PACE STRIDE P ANG MAX 160.00 310.00 180.00 MAX 94.00 151.00 180.00 MIN 70.00 135.00 125.00 MIN 59.00 121.00 150.00 AVG 94.44 179.38 156.00 AVG 68.80 130.25 168.00 SD 16.02 27.18 14.00 SD 14.34 14.08 13.00

Table 3. Footprint morphometrics of B. patagonicus. Cases with a narrow posterior margin of the footprint. 6 footprints measured. Measures in cm.

FL FW DIV ANG II-III ANG L II L III L IV W II W III W IV III-IV MAX 28.00 19.00 57.00 35.00 30.00 6.50 16.00 8.00 3.30 5.00 3.50 MIN 26.00 15.50 50.00 21.00 20.00 2.50 11.00 3.00 2.00 4.30 2.00 AVG 27.58 17.42 52.00 28.00 24.00 4.67 12.92 4.88 2.72 4.80 2.73 SD 0.80 1.24 3.00 5.00 4.00 1.60 1.69 1.70 0.47 0.32 0.54

281 mm (maximum length 400 mm, minimum length 200 mm). an elongate posterior margin. Deferrariischnium mapuchensis The average total width is 191 mm (maximum width 330 mm, Calvo, 1991 from the Ezequiel Ramos Mexía Dam results also minimum width 120 mm). The average inter-digital span be- comparable with some of the footprints in the elongate poste- tween digits II-IV is 55º although it varies between 82º-36º. rior margin. However, D. mapuchensis records a longer digit The footprints with a rounded posterior margin have a long III impression compared to the lateral digit (II, IV) impressions pace (average pace length 944 mm, stride length 1793 mm, and is markedly smaller (approximately 10 x 17 cm in width and pace angle 156º) while those of an elongate posterior and length, respectively). margin of the footprint have a shorter pace (average pace The material of the Candeleros Formation is also compa- length 688 mm, stride length1302 mm, and pace angle 168º). rable to Anchisauripus Lull, 1904 on its general morphology The footprints are assigned to the category 1-3 of the preser- and configuration of digital impressions. Although it differs on vation scale proposed by Marchetti et al. (2019). its size range (20-40 cm in length for B. patagonicus and 15- Comments: The material herein described was previously 25 cm in length for Anchisauripus). The footprints are compa- assigned to Irenesauripus isp. by Krapovickas (2010) due to rable in size to Eubrontes Hitchcock, 1845 although it differs the footprints adjust to general description and dimensions of on the sorter relative length of digit III, respect to the lateral Irenesauripus Sternberg 1932. However, the larger and curved digits and on the wider impression of the digits. impression of digit III results characteristic of B. patagonicus. Recently, Calvo and Rivera (2018) mentioned the material of cf. Brontopodus isp. Cañadón de las Campanas as Bressanichnus patagonicus Figs. 6 and 7. Table 5. and herein we agree. However, the material of Balneario Villa Material: Numerous footprints preserved in situ at Bal- El Chocón and Cañadón de las Campanas are bigger than the neario Villa El Chocón and Cañadón de las Campanas. holotype described for Picun Leufú. B. patagonicus presents Description: Footprints of a quadruped animal with im- a rounded posterior margin of the footprint as well as most of pressions of the forefoot of sub-circular to kidney shape and the material included herein, although some footprints have hindfoot impressions sub-circular to triangular shape. In both

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of trackway with a PTR of 22.8 - 24.7 %. The footprints are assigned to the categories 1-2 of the preservation scale proposed by Marchetti et al. (2019). Comments: Several authors suggested that sauropod trackways can be placed in two general categories: narrow-gauge and wide-gauge (e.g., Farlow et al. 1989, Farlow 1992, Lockley et al. 1994b, Wilson and Carrano 1999) which mostly determine two ichnogenera Parabrontopodus (Lockley et al. 1994a) and Brontopodus (Farlow et al. 1989), respectively. On Parabrontopodus trackways the manus and pes im- prints are placed nearby or at the midline of the trackways and the manus preserve the pollex impression. On the contrary, on Brontopodus the impressions of the sets manus-pes are well separated from the midline and they lack pollex imprint. The material preserved at Cañadón las Campanas and Villa El Chocón lacks morphological details such as digital impressions. However, a wide-gauge pattern is identified on trackway fragments. The morphology of the individual footprints, the manus-pes relationship and the putative pace and trackway fragments relate the footprint with the Brontopodus pattern as in Krapovickas (2010). The ichnotaxa Sauropodichnus giganteus proposed by Calvo (1991) and emended in (1999) is considered nomen dubium by Lockley et al. (1994a). As mentioned by Calvo (1999) both ichnotaxa (Brontopodus and Sau- ropodichnus) are strongly comparable. The other sauropods ichnotaxon erected for the Late Cretaceous of Argentina is Titanopodus mendozensis (González Riga and Calvo 2009). Figure 5. Bressanichnus patagonicus tracks and trackways recorded at Tl1 Cañadón de las Campanas. However, T. mendozensis differs from cf. S. giganteus on the manus impression of crescent shape with strongly asymmet- manus and pes digital impressions are not observed. Manus rical contour and acuminate and thinner external border. In impressions are wider than long (average length 381 mm, av- addition, cf. Brontopodus differs from Calorckosauripus lazari erage width 735 mm), are placed in front of the hindfoot im- from the Late Cretaceous (Maastrichtian) of Cal Orck’o, Sucre pression, and are smaller than the pes impressions. The hind Bolivia in the lower heteropody, the outward rotation of the foot impressions are slightly longer than wide (average length manus, and the quadrangular shape of the pes in C. lazari 817 mm, average width 960 mm). A few examples show the (Meyer et al. 2018). posterior margin of the foot narrower than the anterior margin. Both manus and pes dimensions vary depending on the pres- Table 5. Footprint morphometrics of cf. Brontopodus isp. 9 set m-p mea- ervational context. The pes footprints produced in a soft and sured. Measures in cm. plastic substrate are preserved as sub-circular impressions of LT AT 120 to 140 cm in diameter and 25 cm in depth. The heteropo- m p m p dy in trackways is marked (36.3 - 42.7 %), being manus less MAX 440.0 860.00 830.0 1050.0 than half the area of the pes. Due to the fragmentary expo- MIN 290.0 750.00 610.0 830.0 sure of the outcrops, complete and large trackways are not AVG 381.1 817.5 735.6 960.0 observed. Numerous manus-pes sets are isolated in the same SD 59.5 35.8 78.9 80.2 surface and, in most cases, they correspond to trackways that only preserved one side of the body. However, manus-pes set Large U-shaped tridactyl footprints of both (left and right) sides of the body are observable in Figs. 6 and 8. Tables 6 and 7. two short trackways (Fig. 6b) suggesting a wide-gauge type Material: 37 footprints in 5 trackways preserved at Bal-

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Figure 6. Tetrapod footprints preserved at Balneario Villa El Chocón: a) cf. Brontopodus isp. preserved at Tl3; b) cf. Brontopodus isp. and B. patagonicus preserved at Tl2; c) B. patagonicus and large U-shape tridactyl footprints preserved at Tl1.

Table 6. Footprint morphometrics of large U-shaped tridactyl footprints. Cases with a narrow posterior margin of the footprint. 37 footprints measured. Measures in cm. FL FW DIV ANG II-III ANG L II L III L IV W II W III W IV III-IV

MAX 90.00 74.00 72.00 40.00 35.00 66.00 90.00 78.00 54.00 28.00 21.00 MIN 54.00 51.00 45.00 20.00 20.00 46.00 48.00 28.00 14.00 15.00 8.00 AVG 72.68 63.30 56.00 28.00 28.00 58.44 72.54 60.79 29.95 21.43 17.14 SD 10.37 5.13 7.00 6.00 4.00 5.29 13.72 7.91 16.57 3.16 4.05

Table 7. Trackway morphometrics of large U-shaped tridactyl footprints. 5 age total width is 633 mm (maximum width 740 mm, minimum trackways measured. Measures in cm. width 510 mm). The average inter-digital span between digits II-IV is 56º although it varies between 72º-45º. The average PACE STRIDE P ANG pace length is 1830 mm, the average stride length is 3587 MAX 200,00 382,00 172,00 mm, and the pace angulation is in average 161º. The foot- MIN 160,00 327,00 150,00 AVG 183,00 358,78 160,89 prints are assigned to the category 1 of the preservation scale SD 7,47 12,71 5,60 proposed by Marchetti et al. (2019). Comments: These material, recorded at Balneario Villa neario Villa El Chocón. El Chocón, is ascribed to Limayichnus major by Calvo and Description: Tridactyl footprints of a biped animal of large Rivera (2018). Detailed taphonomic analysis of the footprints size. The impression of the digit III is longer than the later- show that they were produced in a highly-bioturbated soft al ones. The impression of the claws is present although is substrate that prevented the preservation of morphological not well defined and in some poorly preserved examples it is details allowing the precise characterization of the producer’s blunt. In most of the footprints, digits II and IV are connected, autopodial morphology (Krapovickas 2010). Díaz-Martínez et so the posterior margin of the footprint is U-shaped. al. (2015) consider L. major as nomen dubium due to the ab- The average total length of the footprints is 726 mm (max- sence of diagnostic features and consider the footprints can- imum length 900 mm, minimum length 540 mm). The aver-

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Figure 7. Bearing levels of cf. Brontopodus isp. at Cañadón de las Campanas: a) Tl2; b) Tl5; c) cf. Brontopodus isp. preserved in mudstones of Tl2. Note the sub-circular manus impressions (m) and oval pes impressions (p). scale 30 cm; d) cf. Brontopodus isp. preserved in fine sandstones of Tl2. Note the kidney-like manus impressions (m) and the subtriangular pes impressions (p) with a narrow posterior margin of the foot. scale 10 cm.

not be assigned neither to theropod or ornithopod ichnotaxa. Some examples are similar to Tyrannosauripus from the Up- Moreover, they consider it to display a similar morphology to per Cretaceous of the USA, although it presents the impres- the ornithopod ichnogenus Caririchnium Leonardi, 1984. In sion of digit I, absent in large U-shaped footprints (Lockley South America, other Cretaceous large-sized tridactyl foot- and Hunt 1995). prints are recorded in Querulpa Chico (Peru) and Chacarilla (Chile); both tracksites of Early Cretaceous age (Moreno et Medium-sized tridactyl footprints al. 2012). The large tridactyl footprints of Querulpa Chico and Fig. 9a, c. Table 8. Chacarilla display a considerable smaller size than Balneario Material: 11 footprints preserved in situ at Villa El Chocón Villa El Chocón large tridactyl footprints (TL 59 ± 5 cm vs. Description. Tridactyl footprints functionally mesaxon- 72.68 ±10.37 cm; 47 ±13 cm vs 72.68 ±10.37 cm, respec- ic with narrow digital impressions when the digit width rep- tively). In addition, digits are slenderer and lack the typical resents a 10% of the total width of the footprint. The footprints U-shaped outline of the footprints. are slightly longer than wide (maximum length 147 mm, min- They are also comparable on its general morphology and imum length 124 mm). Total digit divarication varies between size to large tridactyl footprints produced by tyrannosaurids 73º and 102º. They present claw marks and lacks hallux im- from the Upper Cretaceous of the USA (Manning et al. 2008). pression. A rhomboidal impression is placed on the posterior

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Table 8. Footprint and trackway morphometrics of Medium size footprints. 11 footprints measured within 1 trackway. Measures in cm

FL FW DIV L II L III L IV W II W III W IV PACE STRIDE P ANG

MAX 16.7 13.9 102 10.4 16.7 10.61 1.3 2.3 1.5 70.0

MIM 10.5 10.08 73 5.4 10.5 5.5 0.5 0.3 0.1 64.5

AVG 14.7 12.4 87 8.4 14.7 8.8 0.7 1.2 0.7 67.25 133 170 SD 2.19 1.19 1.17 1.74 2.15 1.65 0.29 0.57 0.41 3.88

Figure 9. Small- and medium-sized tridactyl footprints preserved at Villa El Chocón: a) Medium-sized tridactyl footprints; b) Small-sized tridactyl footprint; c) map of tracks and trackways of small and medium-sized tridactyl footprints.

margin of the footprint where digits converge. Digit III is longer than the lateral ones (II and IV) which are sub equal in length. Small-sized tridactyl footprint The average pace is 670 mm and the average stride is 1330 Fig. 9b-c. mm. The footprints are assigned to the category 1 of the pres- Material: One footprint preserved in situ at Villa El Chocón. ervation scale proposed by Marchetti et al. (2019). Description: One isolated footprint preserved at the same Comments: The footprints differ from Aquatilavipes Cur- level than the medium-sized tridactyl footprint. The footprint rie, 1981 Barrosopus Coria et al., 2002 and Yacoraitichnus is slightly longer than wide, 75 mm long and 64 mm wide. It Alonso and Marquillas, 1986 in the smaller divarication angle. has delicate digital impressions, claw marks, II-IV interdigital Saurexallopus Harris, 1998 are bigger footprints and have angle of 100º, and lack of hallux impression. Lateral digits a well-preserved hallux impression. Irenichnites Sternberg, are shorter than the central one. The footprints are assigned 1932 and Magnoavipes Lee, 1997 are bigger footprints and to the category 1 of the preservation scale proposed by Mar- have a major length-wide ratio. Columbosauripus Sternberg, chetti et al. (2019) 1932 has a similar size and length-wide ratio but smaller di- Comments: The footprints are comparable to Yacoraitich- vergence angle. nus and Aquatilavipes in its delicate digital impressions, an

456 Revista de la Asociación Geológica Argentina 77 (3): 447-462 (2020) interdigital angle greater than 95º and, in lacking the hallux deleroichnus canalei Calvo and Rivera, 2018. Recently, five impression (Currie 1981, Alonso and Marquillas 1986, Lock- new non-avian theropod trackways were documented at Agua ley et al. 1992, Mccrea and Sarjeant 2001). de Tuco area, Neuquén province (Heredia et al., 2020). They were provisionally assigned to aff. Asianopodus pulvinicalx and assigned to abelisaurid theropods based on symmetric DISCUSSION impression of the footprint most likely involving a robust meta- tarsian III and poorly developed metatarsians II and IV. The tetrapod footprints preserved in the Candeleros For- The large U-shaped tridactyl footprints from Villa El mation at Cañadón de las Campanas, Balneario El Chocón Chocón area and Cañadón de las Campanas are highly com- and Villa El Chocón are mostly attributed to non-avian thero- patible with Limayichnus major from the nearby Picun Leufú pods of varied sizes. Bressanichnus patagonicus record mor- locality. L. major was originally interpreted by Calvo (1991) phological traits and general dimensions that point toward a as produced by large ornithopod dinosaurs mostly based medium- to large-sized non-avian theropod dinosaur. These on the absence of claw marks and the blunt anterior margin are tridactyl pedal prints of a bipedal animal with impression of the footprints. The taphonomic study of the footprints by of digit III longer than II and IV and the presence of a pro- Krapovickas (2010) revealed the footprints were produced in nounced ungual claw mark (Thulborn 1990, Carrano and Wil- a strongly bioturbated soft substrate, both subaqueous and son 2001). In addition, in well-defined footprints produced on exposed to air. As a result, the morphological detail expressed firm substrates of the Candeleros Formation and with almost in the footprints shows a low fidelity to the trackmaker pedal non-existent post formational modifications (i.e., wind or water anatomy that neither allows a certain trackmaker identification erosion, cracking, etc.) it is preserved a complete impression nor sustains strongly supported ichnotaxa. Isolated footprints of digit IV, while the metatarsophalangeal joint of digits II and recorded at Balneario Villa El Chocón show claw marks and III is placed above the ground in a digitigrade position (Krapo- asymmetric posterior margin of the footprints with a notch vickas 2010) (Fig. 3b). This generates an asymmetric poste- behind digits II-III, pointing towards a large theropod dino- rior margin of the footprint classically produced by non-avian saur as putative producer. In addition, several authors (Mey- theropods and basal ornithischians (Farlow et al. 2000). er 2000, Krapovickas 2010, Apesteguía and Gallina 2011, The material herein ascribed to B. patagonicus presents Díaz-Martínez et al. 2015) suggested a theropod affiliation of within the same trackways varying morphologies of the pos- the footprints and, moreover, Apesteguía and Gallina (2011) terior margin of the footprint, reason why it is not considered suggested carcharodontosaurid dinosaurs as possible track- a stable and diagnostic feature. This variability could repre- maker. It is not uncommon that large theropod footprints with sent distinctive locomotor postures of the same producer at low fidelity of the trackmaker autopodium are misinterpreted varying gaits and changing behavior. Most of the footprints as ornithopod dinosaur footprints or even more distant taxo- have a wide and rounded posterior margin and those of elon- nomic groups. So far, large U-shaped tridactyl footprints are gate margins are less frequently recorded (Tables 1, 3). The herein interpreted as most likely produced by large theropod footprints with elongate posterior margin probably represent a dinosaurs. The synapomorphies of the autopodium expressed more complete impression of the foot, with a total impression on the footprints do not allow a farther certain interpretation. of digit IV. A preliminary study evaluated the morphological However, the size of the footprints, still enlarged by the pres- variation within B. patagonicus and its link to gait speed (as ervation style, results coincident with those of carcharodon- pace length), substrate consistency at the time of footprint im- tosaurid dinosaurs recorded at the Candeleros Formation. plantation and post exhumation weathering of the footprints Another large-sized dinosaur footprint recorded in the unit (Farina et al. 2019). The study did not show a clear associa- corresponds to A. astigarrae, with an average footprint length tion with any of these putative causes, suggesting it is more and width of 48.5 cm and 43.5 cm, respectively (Calvo 1991, likely linked to varying postural gaits and changing behavior. Calvo and Rivera 2018). They were also tentatively assigned The Candeleros Formation has an extensive record of to carcharodontosaurid dinosaurs (Calvo and Rivera 2018). ichnotaxa attributed to non-avian theropods. Most of the foot- Due to the comparable size and morphology of the footprints prints were documented along the coast of the Ezequiel Ra- it is not discarded that large U-shaped tridactyl footprints (pre- mos Mexía Dam and corresponds to Abelichnus astigarrae viously L. major) represent a preservational variant of A. asti- Calvo, 1991, Bressanichnus patagonicus, Deferrariischnium garrae. However, that hypothesis needs yet to be tested. mapuchensis, Picunichnus benedettoi Calvo, 1991, and Can- Most of the medium-sized tridactyl footprints are preserved

457 Revista de la Asociación Geológica Argentina 77 (3): 447-462 (2020) as true tracks and record collapse structures as they were pro- maker. Wilson and Carrano (1999) stated that titanosaurs duced in soft to soap grounds (Krapovickas 2010) (Fig. 9). A (specially saltasaurines) are wide-gauge sauropods due to few footprints seem to be undertracks evidenced by its major synapomorphies as an outwardly angled femoral posture, dimensions and lower depths. Even though their morphology beveled knee condyles, and asymmetrical femoral midshaft does not completely evidence the autopodium anatomy of the causing wide foot stances in this large graviportal animal. The trackmaker, certain traits are evident. They present numer- hypothesis that “titanosauriforms were capable of a greater ous traits that relate them with avian theropods as defined by degree of hind limb abduction and adduction” was corroborat- Currie (1981), Lockley et al. (1992), Doyle et al. (2000), and ed quantitatively by Ullmann et al. (2017). The wet interdune Mccrea and Sarjeant (2001). They have a) narrow digit im- and playa-lake deposits of the Candeleros Formation results pressions, b) wide II-IV interdigital angle, c) a metatarsal pad a propitious environment for the formation and preservation impression where digits converge, and d) claw marks (Krapo- of footprints, but unfortunately they are not adequate for foot- vickas et al. 2007). However, the thin digit impressions are print morphological details (Mancuso et al. 2007). As mention most likely an artifact due to the collapse of sediments within above cf. Brontopodus from Picún Leufú was previously in- the footprints and at least claw marks are not an exclusive terpreted as a wide-gauge trackway (S. giganteus in Calvo, avian trait. Moreover, there are other traits typical of Mesozoic 1999) and compared to Brontopodus which lacks a pollex avian footprints as pointed by the previously mentioned au- imprint and the impression of the sets manus-pes are well thors that are not present in the medium-sized footprints of the separated from the midline. Heredia et al. (2019) interpreted Candeleros Formation. They have a) interdigital divergence cf. Brontopodus (S. giganteus) as a medium-gauge trackway angle II-IV of 100º-120º or more, b) small size, c) length/width proposed through the indirect calculation of the pes-trackway ratio of less than 1. Nevertheless, all these footprint morpho- ratio (PTR), as proposed by Romano et al. (2007). Howev- logical traits point specifically toward shorebirds rather than er, the authors mentioned that the ratio found is very close bird footprints in general. For example, certain cursorial birds to that of wide gauge trackways. Several authors pointed out (i.e., Rheiformes and Casuariiformes) lack delicate digits and that some sauropod trackways exhibit both narrow-gauge and the total divergence angle between digits II-IV is clearly less wide-gauge stances, suggesting that the stance is not exclu- than 90º (Farlow et al., 2000); while some footprints attributed sively linked to the producer’s identity but also to changes to non-avian theropods as Magnoavipes and Saurexallopus in substrate consistency, speed, and particular behaviors or have interdigital angles as wide as any Mesozoic bird footprint change in direction (Romano et al. 2007, Meyer et al. 2018). (Harris, 1998). Martin et al. (2014) addressed a similar prob- According to Ullmann et al. (2017), the wide-gauge posture lem by distinguishing between similarly sized non-avian and afforded titanosauriforms greater static and dynamic stability avian dinosaur tracks in Early Cretaceous (Albian) of Victoria, by providing wider stability triangles while moving. The ability Australia. All this suggests that there is a wide morphological of these giant graviportal animals of narrowing gauge if neces- superposition between avian and non-avian theropod foot- sary (e.g., turning, increasing speed) has not been proved to prints that needs to be treated more carefully. Thus, herein be anatomically prevented. The opposite (i.e., narrow-gauge we interpret the medium-sized tridactyl footprints as produced sauropods producing wide-gauge trackways) seems more un- by a medium to small non-avian theropod, even though birds likely, in despite both premises have still to be tested. Anoth- cannot be completely discarded as producers. er sauropod trackway has been recorded at the Candeleros As in the previously mentioned case, the small tridactyl Formation at the Agua de Tuco locality, between Chos Malal footprints have some morphological traits typically attributed and Añelo cities, Neuquén province, Argentina (Heredia et al. to avian theropods as delicate digit impressions, wide inter- 2019). The material corresponds to one trackway not assigned digital II-IV angle and, small size even though they are not to any ichnotaxon due to the absence of clear anatomical de- exclusive of birds. tails. However, it was possible to determine a narrow-gauge The footprints assigned to cf. Brontopodus are with cer- type of trackway and it was suggested as produced by a large- tainty assigned to sauropod dinosaurs and tentatively to ti- sized rebbachisaurid diplodocoid (Heredia et al. 2019). This is tanosaurs. The incomplete exposure of the tracking levels based on the idea that narrow-gauged trackways have been avoids a profound evaluation of the trackway patterns. How- typically attributed to diplodocoids in the fossil record and in ever, the record of isolated manus-pes sets well apart from the record of the diplodocoids in the same stratigraphic unit the midline on trackway fragments and PTR of 22.8 – 24.7 (see Heredia et al. 2019). %, (Fig. 6b), points towards a wide-gauge sauropod track- The bone dinosaur record of the Candeleros Formation is

458 Revista de la Asociación Geológica Argentina 77 (3): 447-462 (2020) probably one of the most diverse in any stratigraphic unit of las Campanas shows a high abundance of footprints but still South America (Canale et al. 2016). It comprises the titano- a low diversity of morphologies (i.e., ichnotaxa). The footprint saur Andesaurus delgadoi (Calvo and Bonaparte 1991), the record suggests the presence of two large-sized dinosaurs: a rebbachisarids Limaysarus tessonei, Rayososaurus agrio- sauropod that produced cf. Brontopodus (S. giganteus) and ensis, and Nopcsaspondylus alarconensis (Calvo and Sal- a non-avian theropod producing large U-shaped tridactyl foot- gado 1995, Carballido et al. 2010), and a large diversity of prints (L. major). The record of short trackways that reveal a theropods.. The meat-eating dinosaur record of Candeleros wide-gauge foot stance point toward titanosaur sauropods includes the large abelisaurid Ekrixinatosaurus novasi (Calvo as the most likely producers of cf. Brontopodus. Coinciden- et al. 2004), the giant carcharodontosaurid Giganotosaurus tal interpretations, that is comparable sized animals pointed carolinii (Coria and Salgado, 1995), the basal coelurosaur out by the bone record of the same stratigraphic unit, could Bicentenaria argentina (Novas et al. 2012), the alvarezsaur suggest that large U-shaped tridactyl footprints were produced Alnashetri cerropoliciencis (Makovicky et al. 2012), and the by carcharodontosaurid dinosaurs. Within smaller footprint unenlagiid Buitreraptor gonzalezorum (Makovicky et al. morphologies, the most abundantly represented is the medi- 2005). Despite this extensive and diverse dinosaur record, um- to large-sized non-avian theropod footprint (Bressanich- the remains recovered stratigraphically near the track-bearing nus patagonicus). This material includes varying morphologies levels only includes the titanosaur sauropod Andesaurus del- of the posterior margin of the footprints, most likely involving gadoi near the Balneario of Villa El Chocón. varying postural gaits and changing behavior. Finally, the VLC As a total, the ichnologic record of dinosaurs of the Cande- record includes two less represented medium- and small-sized leros Formation comprises large-sized footprints (≈ 35-65 cm non-avian theropod footprints without taxonomic assignment. in length), attributed to non-avian theropods as A. astigarrae and large U-shaped tridactyl footprints (L. major) (Calvo 1991, Krapovickas 2010), medium- to large-sized footprints (≈ 22-42 ACKNOWLEDGMENTS cm in length) attributed to non-avian theropods corresponding to B. patagonicus and Aff. Asianopodus pulvinicalx (Krapovick- We thank the editors G.S. Bressan and D.E, Fernandez for as 2010, Calvo and Rivera 2018, Heredia et al. 2020), me- inviting us to contribute to this special issue on Recent devel- dium-sized tridactyl footprints, D. mapuchensis, and P. ben- opments in Argentine ichnology. l We thank the reviewers An- edettoi as footprints of medium size (≈ 13-22 cm in length) thony Martin and Matteo Beldevere for their useful comments attributed to non-avian theropods (Calvo 1991, Calvo and and suggestions. We are also thankful to Alejandro Haluza, Rivera 2018). Finally, small tridactyl footprints and C. canalei Adriana Mancuso and Leandro Martinez for their assistance corresponding to footprints of small size (≈ 7-13 cm in length) and comradeship during field work and to Municipalidad of Vil- attributed to non-avian theropods (Calvo and Rivera 2018). la El Chocón for their support on fieldtrips. To Luis Perouene There are sauropod trackways preserved pointing towards two and the Zarza family for allowing us to enter their property on gait styles: the wide-gauge cf. Brontopodus (S. giganteus) and Cañadón de las Campanas. We also thank Javier Ochoa, who the Aguada de Tuco narrow-gauge trackway, both with large- found the small and medium sized tridactyl footprints at Villa sized footprints (80-100cm in length). Sousaichnium monetae El Chocón. Calvo 1991 has been attributed to iguanodontid ornithopods (Calvo and Bonaparte 1991, Calvo 1999), however other au- REFERENCES thors do not agree and regard it as a theropod track and a Alonso, R.N., and Marquillas, R.A. 1986. Nueva localidad con huellas junior synonym of Limayichnus (Meyer 2000, Díaz-Martínez et de dinosaurios y primer hallazgo de huellas de aves en la Formación al. 2015). 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